Solar photovoltaic electricity systems are becoming more popular. These systems allow homeowners, farmers, business owners and non-profits to generate some or all of their own electricity on-site, while still conveniently connected with the electric utility grid. Solar equipment is expensive and includes solar modules and inverters.
Solar PV infrastructure includes solar PV modules and inverters. The modules use silicon cells that create direct current (DC) when exposed to sunlight (photons). Direct current (DC) is delivered to solar inverters, which invert the DC power to grid-quality AC power. The AC output is fed into a main service panel or sub panel, and can also feed back to the utility grid. The energy can be used directly by loads served by the panel, and excess electricity can flow out onto the utility grid and turn the meter “backwards”.
Photovoltaic (PV) solar panels are a source of DC electrical energy when the level of light intensity (irradiance) falling on them is sufficient. This DC energy cannot be utilized by the utility grid until it is converted into a reasonable facsimile of a 60 Hz sinusoidal wave, which will be referred to as “60 Hz AC”, or simply “AC”. The “machine” that accomplishes this will be referred to as an “inverter”. A solar PV installation can consist of multiple PV arrays connected in various series and parallel modes to multiple inverters. When more than a single inverter is employed, the inverters interact only at the 60 Hz AC outputs. The DC inputs to each inverter are independent from the inputs to other inverters. Paralleling dissimilar DC inputs into the same inverter can lower output efficiency. This is because an algorithm within each inverter is employed to calculate and track the optimal contribution of that inverter to the total AC energy output. The energy is delivered to the service panel and potentially to the utility grid. The utility grid is often referred to as “the grid”. Generally the grid can absorb all the AC that is fed to it by the inverters.
When solar irradiance is sufficiently low, the DC voltage provided by the PV solar panels drops below operating levels. As a result, the AC output of the inverters goes to zero and they are programmed to turn themselves off. This certainly occurs at night, but can also occur on very overcast days, as well as days where the PV solar panels are covered with snow, leaves, shadows, etc.